src/src/exim_lock.c

   1 /* A program to lock a file exactly as Exim would, for investigation of
   2 interlocking problems.
   3
   4 Options:  -fcntl    use fcntl() lock
   5           -flock    use flock() lock
   6           -lockfile use lock file
   7           -mbx      use mbx locking rules, with either fcntl() or flock()
   8
   9 Default is -fcntl -lockfile.
  10
  11 Argument: the name of the lock file
  12 */
  13
  14 #include "os.h"
  15
  16 #include <stdio.h>
  17 #include <stdlib.h>
  18 #include <string.h>
  19 #include <signal.h>
  20 #include <errno.h>
  21 #include <time.h>
  22 #include <netdb.h>
  23 #include <fcntl.h>
  24 #include <unistd.h>
  25 #include <utime.h>
  26 #include <sys/utsname.h>
  27 #include <sys/stat.h>
  28 #include <sys/file.h>
  29 #include <pwd.h>
  30
  31 /* Not all systems have flock() available. Those that do must define LOCK_SH
  32 in sys/file.h. */
  33
  34 #ifndef LOCK_SH
  35 #define NO_FLOCK
  36 #endif
  37
  38
  39 typedef int BOOL;
  40 #define FALSE 0
  41 #define TRUE  1
  42
  43
  44 /* Flag for timeout signal handler */
  45
  46 static int sigalrm_seen = FALSE;
  47
  48
  49 /* We need to pull in strerror() and os_non_restarting_signal() from the
  50 os.c source, if they are required for this OS. However, we don't need any of
  51 the other stuff in os.c, so force the other macros to omit it. */
  52
  53 #ifndef OS_RESTARTING_SIGNAL
  54   #define OS_RESTARTING_SIGNAL
  55 #endif
  56
  57 #ifndef OS_STRSIGNAL
  58   #define OS_STRSIGNAL
  59 #endif
  60
  61 #ifndef OS_STREXIT
  62   #define OS_STREXIT
  63 #endif
  64
  65 #ifndef OS_LOAD_AVERAGE
  66   #define OS_LOAD_AVERAGE
  67 #endif
  68
  69 #ifndef FIND_RUNNING_INTERFACES
  70   #define FIND_RUNNING_INTERFACES
  71 #endif
  72
  73 #ifndef OS_GET_DNS_RESOLVER_RES
  74   #define OS_GET_DNS_RESOLVER_RES
  75 #endif
  76
  77 #include "../src/os.c"
  78
  79
  80
  81 /*************************************************
  82 *             Timeout handler                    *
  83 *************************************************/
  84
  85 static void
  86 sigalrm_handler(int sig)
  87 {
  88 sig = sig;      /* Keep picky compilers happy */
  89 sigalrm_seen = TRUE;
  90 }
  91
  92
  93
  94 /*************************************************
  95 *           Give usage and die                   *
  96 *************************************************/
  97
  98 static void
  99 usage(void)
 100 {
 101 printf("usage: exim_lock [-v] [-q] [-lockfile] [-fcntl] [-flock] [-mbx]\n"
 102        "       [-retries <n>] [-interval <n>] [-timeout <n>] [-restore-times]\n"
 103        "       <file name> [command]\n");
 104 exit(1);
 105 }
 106
 107
 108
 109 /*************************************************
 110 *         Apply a lock to a file descriptor      *
 111 *************************************************/
 112
 113 static int
 114 apply_lock(int fd, int fcntltype, BOOL dofcntl, int fcntltime, BOOL doflock,
 115     int flocktime)
 116 {
 117 int yield = 0;
 118 int save_errno;
 119 struct flock lock_data;
 120 lock_data.l_type = fcntltype;
 121 lock_data.l_whence = lock_data.l_start = lock_data.l_len = 0;
 122
 123 sigalrm_seen = FALSE;
 124
 125 if (dofcntl)
 126   {
 127   if (fcntltime > 0)
 128     {
 129     os_non_restarting_signal(SIGALRM, sigalrm_handler);
 130     alarm(fcntltime);
 131     yield = fcntl(fd, F_SETLKW, &lock_data);
 132     save_errno = errno;
 133     alarm(0);
 134     errno = save_errno;
 135     }
 136   else yield = fcntl(fd, F_SETLK, &lock_data);
 137   if (yield < 0) printf("exim_lock: fcntl() failed: %s\n", strerror(errno));
 138   }
 139
 140 #ifndef NO_FLOCK
 141 if (doflock && (yield >= 0))
 142   {
 143   int flocktype = (fcntltype == F_WRLCK)? LOCK_EX : LOCK_SH;
 144   if (flocktime > 0)
 145     {
 146     os_non_restarting_signal(SIGALRM, sigalrm_handler);
 147     alarm(flocktime);
 148     yield = flock(fd, flocktype);
 149     save_errno = errno;
 150     alarm(0);
 151     errno = save_errno;
 152     }
 153   else yield = flock(fd, flocktype | LOCK_NB);
 154   if (yield < 0) printf("exim_lock: flock() failed: %s\n", strerror(errno));
 155   }
 156 #endif
 157
 158 return yield;
 159 }
 160
 161
 162
 163 /*************************************************
 164 *           The exim_lock program                *
 165 *************************************************/
 166
 167 int main(int argc, char **argv)
 168 {
 169 int  lock_retries = 10;
 170 int  lock_interval = 3;
 171 int  lock_fcntl_timeout = 0;
 172 int  lock_flock_timeout = 0;
 173 int  i, j, len;
 174 int  fd = -1;
 175 int  hd = -1;
 176 int  md = -1;
 177 int  yield = 0;
 178 time_t now = time(NULL);
 179 BOOL use_lockfile = FALSE;
 180 BOOL use_fcntl = FALSE;
 181 BOOL use_flock = FALSE;
 182 BOOL use_mbx = FALSE;
 183 BOOL verbose = FALSE;
 184 BOOL quiet = FALSE;
 185 BOOL restore_times = FALSE;
 186 char *filename;
 187 char *lockname = NULL, *hitchname = NULL;
 188 char *primary_hostname;
 189 const char *command;
 190 struct utsname s;
 191 char buffer[256];
 192 char tempname[256];
 193
 194 /* Decode options */
 195
 196 for (i = 1; i < argc; i++)
 197   {
 198   char *arg = argv[i];
 199   if (*arg != '-') break;
 200   if (strcmp(arg, "-fcntl") == 0) use_fcntl = TRUE;
 201   else if (strcmp(arg, "-flock") == 0) use_flock = TRUE;
 202   else if (strcmp(arg, "-lockfile") == 0) use_lockfile = TRUE;
 203   else if (strcmp(arg, "-mbx") == 0) use_mbx = TRUE;
 204   else if (strcmp(arg, "-v") == 0) verbose = TRUE;
 205   else if (strcmp(arg, "-q") == 0) quiet = TRUE;
 206   else if (strcmp(arg, "-restore-times") == 0) restore_times = TRUE;
 207   else if (++i < argc)
 208     {
 209     int value = atoi(argv[i]);
 210     if (strcmp(arg, "-retries") == 0) lock_retries = value;
 211     else if (strcmp(arg, "-interval") == 0) lock_interval = value;
 212     else if (strcmp(arg, "-timeout") == 0)
 213       lock_fcntl_timeout = lock_flock_timeout = value;
 214     else usage();
 215     }
 216   else usage();
 217   }
 218
 219 if (quiet) verbose = FALSE;
 220
 221 /* Can't use flock() if the OS doesn't provide it */
 222
 223 #ifdef NO_FLOCK
 224 if (use_flock)
 225   {
 226   printf("exim_lock: can't use flock() because it was not available in the\n"
 227          "           operating system when exim_lock was compiled\n");
 228   exit(1);
 229   }
 230 #endif
 231
 232 /* Default is to use lockfiles and fcntl(). */
 233
 234 if (!use_lockfile && !use_fcntl && !use_flock && !use_mbx)
 235   use_lockfile = use_fcntl = TRUE;
 236
 237 /* Default fcntl() for use with mbx */
 238
 239 if (use_mbx && !use_fcntl && !use_flock) use_fcntl = TRUE;
 240
 241 /* Unset unused timeouts */
 242
 243 if (!use_fcntl) lock_fcntl_timeout = 0;
 244 if (!use_flock) lock_flock_timeout = 0;
 245
 246 /* A file name is required */
 247
 248 if (i >= argc) usage();
 249
 250 filename = argv[i++];
 251
 252 /* Expand file names starting with ~ */
 253
 254 if (*filename == '~')
 255   {
 256   struct passwd *pw;
 257
 258   if (*(++filename) == '/')
 259     pw = getpwuid(getuid());
 260   else
 261     {
 262     char *s = buffer;
 263     while (*filename != 0 && *filename != '/')
 264       *s++ = *filename++;
 265     *s = 0;
 266     pw = getpwnam(buffer);
 267     }
 268
 269   if (pw == NULL)
 270     {
 271     printf("exim_lock: unable to expand file name %s\n", argv[i-1]);
 272     exit(1);
 273     }
 274
 275   if ((int)strlen(pw->pw_dir) + (int)strlen(filename) + 1 > sizeof(buffer))
 276     {
 277     printf("exim_lock: expanded file name %s%s is too long", pw->pw_dir,
 278       filename);
 279     exit(1);
 280     }
 281
 282   strcpy(buffer, pw->pw_dir);
 283   strcat(buffer, filename);
 284   filename = buffer;
 285   }
 286
 287 /* If using a lock file, prepare by creating the lock file name and
 288 the hitching post name. */
 289
 290 if (use_lockfile)
 291   {
 292   if (uname(&s) < 0)
 293     {
 294     printf("exim_lock: failed to find host name using uname()\n");
 295     exit(1);
 296     }
 297   primary_hostname = s.nodename;
 298
 299   len = (int)strlen(filename);
 300   lockname = malloc(len + 8);
 301   sprintf(lockname, "%s.lock", filename);
 302   hitchname = malloc(len + 32 + (int)strlen(primary_hostname));
 303
 304   /* Presumably, this must match appendfile.c */
 305   sprintf(hitchname, "%s.%s.%08x.%08x", lockname, primary_hostname,
 306     (unsigned int)now, (unsigned int)getpid());
 307
 308   if (verbose)
 309     printf("exim_lock: lockname =  %s\n           hitchname = %s\n", lockname,
 310       hitchname);
 311   }
 312
 313 /* Locking retry loop */
 314
 315 for (j = 0; j < lock_retries; j++)
 316   {
 317   int sleep_before_retry = TRUE;
 318   struct stat statbuf, ostatbuf, lstatbuf, statbuf2;
 319   int mbx_tmp_oflags;
 320
 321   /* Try to build a lock file if so configured */
 322
 323   if (use_lockfile)
 324     {
 325     int rc, rc2;
 326     if (verbose) printf("exim_lock: creating lock file\n");
 327     hd = open(hitchname, O_WRONLY | O_CREAT | O_EXCL, 0440);
 328     if (hd < 0)
 329       {
 330       printf("exim_lock: failed to create hitching post %s: %s\n", hitchname,
 331         strerror(errno));
 332       exit(1);
 333       }
 334
 335     /* Apply hitching post algorithm. */
 336
 337     if ((rc = link(hitchname, lockname)) != 0)
 338      rc2 = fstat(hd, &statbuf);
 339     (void)close(hd);
 340     unlink(hitchname);
 341
 342     if (rc != 0 && (rc2 != 0 || statbuf.st_nlink != 2))
 343       {
 344       printf("exim_lock: failed to link hitching post to lock file\n");
 345       hd = -1;
 346       goto RETRY;
 347       }
 348
 349     if (!quiet) printf("exim_lock: lock file successfully created\n");
 350     }
 351
 352   /* We are done if no other locking required. */
 353
 354   if (!use_fcntl && !use_flock && !use_mbx) break;
 355
 356   /* Open the file for writing. */
 357
 358   fd = open(filename, O_RDWR + O_APPEND);
 359   if (fd < 0)
 360     {
 361     printf("exim_lock: failed to open %s for writing: %s\n", filename,
 362       strerror(errno));
 363     yield = 1;
 364     goto CLEAN_UP;
 365     }
 366
 367   /* If there is a timeout, implying blocked locking, we don't want to
 368   sleep before any retries after this. */
 369
 370   if (lock_fcntl_timeout > 0 || lock_flock_timeout > 0)
 371     sleep_before_retry = FALSE;
 372
 373   /* Lock using fcntl. There are pros and cons to using a blocking call vs
 374   a non-blocking call and retries. Exim is non-blocking by default, but setting
 375   a timeout changes it to blocking. */
 376
 377   if (!use_mbx && (use_fcntl || use_flock))
 378     {
 379     if (apply_lock(fd, F_WRLCK, use_fcntl, lock_fcntl_timeout, use_flock,
 380         lock_flock_timeout) >= 0)
 381       {
 382       if (!quiet)
 383         {
 384         if (use_fcntl) printf("exim_lock: fcntl() lock successfully applied\n");
 385         if (use_flock) printf("exim_lock: flock() lock successfully applied\n");
 386         }
 387       break;
 388       }
 389     else goto RETRY;   /* Message already output */
 390     }
 391
 392   /* Lock using MBX rules. This is complicated and is documented with the
 393   source of the c-client library that goes with Pine and IMAP. What has to
 394   be done to interwork correctly is to take out a shared lock on the mailbox,
 395   and an exclusive lock on a /tmp file. */
 396
 397   else
 398     {
 399     if (apply_lock(fd, F_RDLCK, use_fcntl, lock_fcntl_timeout, use_flock,
 400         lock_flock_timeout) >= 0)
 401       {
 402       if (!quiet)
 403         {
 404         if (use_fcntl)
 405           printf("exim_lock: fcntl() read lock successfully applied\n");
 406         if (use_flock)
 407           printf("exim_lock: fcntl() read lock successfully applied\n");
 408         }
 409       }
 410     else goto RETRY;   /* Message already output */
 411
 412     if (fstat(fd, &statbuf) < 0)
 413       {
 414       printf("exim_lock: fstat() of %s failed: %s\n", filename,
 415         strerror(errno));
 416       yield = 1;
 417       goto CLEAN_UP;
 418       }
 419
 420     /* Set up file in /tmp and check its state if already existing. */
 421
 422     sprintf(tempname, "/tmp/.%lx.%lx", (long)statbuf.st_dev,
 423       (long)statbuf.st_ino);
 424
 425     if (lstat(tempname, &statbuf) >= 0)
 426       {
 427       if ((statbuf.st_mode & S_IFMT) == S_IFLNK)
 428         {
 429         printf("exim_lock: symbolic link on lock name %s\n", tempname);
 430         yield = 1;
 431         goto CLEAN_UP;
 432         }
 433       if (statbuf.st_nlink > 1)
 434         {
 435         printf("exim_lock: hard link to lock name %s\n", tempname);
 436         yield = 1;
 437         goto CLEAN_UP;
 438         }
 439       }
 440
 441     mbx_tmp_oflags = O_RDWR | O_CREAT;
 442 #ifdef O_NOFOLLOW
 443     mbx_tmp_oflags |= O_NOFOLLOW;
 444 #endif
 445     md = open(tempname, mbx_tmp_oflags, 0600);
 446     if (md < 0)
 447       {
 448       printf("exim_lock: failed to create mbx lock file %s: %s\n",
 449         tempname, strerror(errno));
 450       goto CLEAN_UP;
 451       }
 452
 453     /* security fixes from 2010-05 */
 454     if (lstat(tempname, &lstatbuf) < 0)
 455       {
 456       printf("exim_lock: failed to lstat(%s) after opening it: %s\n",
 457           tempname, strerror(errno));
 458       goto CLEAN_UP;
 459       }
 460     if (fstat(md, &statbuf2) < 0)
 461       {
 462       printf("exim_lock: failed to fstat() open fd of \"%s\": %s\n",
 463           tempname, strerror(errno));
 464       goto CLEAN_UP;
 465       }
 466     if ((statbuf2.st_nlink > 1) ||
 467         (lstatbuf.st_nlink > 1) ||
 468         (!S_ISREG(lstatbuf.st_mode)) ||
 469         (lstatbuf.st_dev != statbuf2.st_dev) ||
 470         (lstatbuf.st_ino != statbuf2.st_ino))
 471       {
 472       printf("exim_lock: race condition exploited against us when "
 473           "locking \"%s\"\n", tempname);
 474       goto CLEAN_UP;
 475       }
 476
 477     (void)chmod(tempname, 0600);
 478
 479     if (apply_lock(md, F_WRLCK, use_fcntl, lock_fcntl_timeout, use_flock,
 480         lock_flock_timeout) >= 0)
 481       {
 482       if (!quiet)
 483         {
 484         if (use_fcntl)
 485           printf("exim_lock: fcntl() lock successfully applied to mbx "
 486             "lock file %s\n", tempname);
 487         if (use_flock)
 488           printf("exim_lock: flock() lock successfully applied to mbx "
 489             "lock file %s\n", tempname);
 490         }
 491
 492       /* This test checks for a race condition */
 493
 494       if (lstat(tempname, &statbuf) != 0 ||
 495           fstat(md, &ostatbuf) != 0 ||
 496           statbuf.st_dev != ostatbuf.st_dev ||
 497           statbuf.st_ino != ostatbuf.st_ino)
 498        {
 499        if (!quiet) printf("exim_lock: mbx lock file %s changed between "
 500            "creation and locking\n", tempname);
 501        goto RETRY;
 502        }
 503       else break;
 504       }
 505     else goto RETRY;   /* Message already output */
 506     }
 507
 508   /* Clean up before retrying */
 509
 510   RETRY:
 511
 512   if (md >= 0)
 513     {
 514     if (close(md) < 0)
 515       printf("exim_lock: close %s failed: %s\n", tempname, strerror(errno));
 516     else
 517       if (!quiet) printf("exim_lock: %s closed\n", tempname);
 518     md = -1;
 519     }
 520
 521   if (fd >= 0)
 522     {
 523     if (close(fd) < 0)
 524       printf("exim_lock: close failed: %s\n", strerror(errno));
 525     else
 526       if (!quiet) printf("exim_lock: file closed\n");
 527     fd = -1;
 528     }
 529
 530   if (hd >= 0)
 531     {
 532     if (unlink(lockname) < 0)
 533       printf("exim_lock: unlink of %s failed: %s\n", lockname, strerror(errno));
 534     else
 535       if (!quiet) printf("exim_lock: lock file removed\n");
 536     hd = -1;
 537     }
 538
 539   /* If a blocking call timed out, break the retry loop if the total time
 540   so far is not less than than retries * interval. */
 541
 542   if (sigalrm_seen &&
 543       (j + 1) * ((lock_fcntl_timeout > lock_flock_timeout)?
 544         lock_fcntl_timeout : lock_flock_timeout) >=
 545           lock_retries * lock_interval)
 546     j = lock_retries;
 547
 548   /* Wait a bit before retrying, except when it was a blocked fcntl() that
 549   caused the problem. */
 550
 551   if (j < lock_retries && sleep_before_retry)
 552     {
 553     printf(" ... waiting\n");
 554     sleep(lock_interval);
 555     }
 556   }
 557
 558 if (j >= lock_retries)
 559   {
 560   printf("exim_lock: locking failed too many times\n");
 561   yield = 1;
 562   goto CLEAN_UP;
 563   }
 564
 565 if (!quiet) printf("exim_lock: locking %s succeeded: ", filename);
 566
 567 /* If there are no further arguments, run the user's shell; otherwise
 568 the next argument is a command to run. */
 569
 570 if (i >= argc)
 571   {
 572   command = getenv("SHELL");
 573   if (command == NULL || *command == 0) command = "/bin/sh";
 574   if (!quiet) printf("running %s ...\n", command);
 575   }
 576 else
 577   {
 578   command = argv[i];
 579   if (!quiet) printf("running the command ...\n");
 580   }
 581
 582 /* Run the command, saving and restoring the times if required. */
 583
 584 if (restore_times)
 585   {
 586   struct stat strestore;
 587   struct utimbuf ut;
 588   stat(filename, &strestore);
 589   i = system(command);
 590   ut.actime = strestore.st_atime;
 591   ut.modtime = strestore.st_mtime;
 592   utime(filename, &ut);
 593   }
 594 else i = system(command);
 595
 596 if(i && !quiet) printf("warning: nonzero status %d\n", i);
 597
 598 /* Remove the locks and exit. Unlink the /tmp file if we can get an exclusive
 599 lock on the mailbox. This should be a non-blocking lock call, as there is no
 600 point in waiting. */
 601
 602 CLEAN_UP:
 603
 604 if (md >= 0)
 605   {
 606   if (apply_lock(fd, F_WRLCK, use_fcntl, 0, use_flock, 0) >= 0)
 607     {
 608     if (!quiet) printf("exim_lock: %s unlinked - no sharers\n", tempname);
 609     unlink(tempname);
 610     }
 611   else if (!quiet)
 612     printf("exim_lock: %s not unlinked - unable to get exclusive mailbox lock\n",
 613       tempname);
 614   if (close(md) < 0)
 615     printf("exim_lock: close %s failed: %s\n", tempname, strerror(errno));
 616   else
 617     if (!quiet) printf("exim_lock: %s closed\n", tempname);
 618   }
 619
 620 if (fd >= 0)
 621   {
 622   if (close(fd) < 0)
 623     printf("exim_lock: close %s failed: %s\n", filename, strerror(errno));
 624   else
 625     if (!quiet) printf("exim_lock: %s closed\n", filename);
 626   }
 627
 628 if (hd >= 0)
 629   {
 630   if (unlink(lockname) < 0)
 631     printf("exim_lock: unlink %s failed: %s\n", lockname, strerror(errno));
 632   else
 633     if (!quiet) printf("exim_lock: lock file removed\n");
 634   }
 635
 636 return yield;
 637 }
 638
 639 /* End */